"One possibility that comes to mind, though, is scattering a bunch of probes around on Venus that don't have imagers of any type (in addition to some that do), in order to get purely compositional data from the surface at a number of places for comparison purposes"

One problem with doing this without a camera is that you may not know the local geological context of the sample you get. Many tessera areas, for instance, have small patches of basalt in low spots, and many plains areas have small cones, ridges or patches of older material protruding through the plains material. Which material are you sampling? The Venera images and compositions we have are compromised a bit in usefulness because it's not really possible to relate them to specific geological units.

Bandwidth is a problem, but it's less of one now than it used to be - not long ago the idea of transmitting a heavily compressed image was anathema, but now it's done quite often. We would be better off with descent imaging, even if horribly compressed, in order to get the exact location of the landing site. And images can be compressed a lot these days.

But, once again, a high-resolution radar orbiter -- combined with the improved tracking that we have now over that for the Veneras -- could identify the landing sites for such landers with enough accuracy to enable the overall geological context of their samples to be determined. (After all, the phenomena Phil describes have been detected entirely on the basis of the Magellan images.)

In that connection, how do you know that there are "small patches of basalt in low spots" in the tesserae? Are these relatively crack-free patches, presumably laid down by later lava flows in the tesserae?

Bruce, yes, lots of tesserae have small ponds of lava in low spots, and fingers of it extending from the plains, a common embayment relationship. They show up clearly in Magellan images, but please don't ask me to unearth one right now! There must be patches of aeolian sediment, dark parabola material or ejecta in low spots, or other complicating factors as well.

The trouble with the high res radar is that, yes, you get better images, but no, you still don't know exactly which spot the lander came down on. Only descent imaging can do that for you, or the very difficult task, likely to be almost impossible on Venus, of matching features in surface panoramas with orbital images. There is no other way to locate a landing site exactly at the scale needed for knowing its geological context. Of course this does not apply in the case of homogeneous plains. In tesserae or any other complex landscape you are still better to go with descent imaging if at all possible, using heavy compression if bandwidth is the issue. I just ran a test, and I can easily reduce a 1 MB TIFF to 25K without compromising its usefulness for site location, probably smaller.

Another possibility is, if the probe transmits at a very high rate, is that after landing, better versions of the images are returned with little loss.

I'm with Phil -- there are really good compression algorithms today that could be used. And you learn so much more if you understand what you landed on (are you measuring dust or a pebble or a lava plain?). If you really don't like having a relay craft, consider that a single image 1000x1000 image could be returned at ~300 bits/second (assuming 8X data compression). Probably not that unrealistic given today's communications technology at both ends.

But I think that the relay more than makes up for the extra complexity. I do remote sensing for my graduate work. Even 30m pixels are incredibly frustrating because they hide so much detail. Venus coverage is even worse.

If you have the relay craft and a roughly 3 hour communications window, you could imagine a mission that takes 30 minutes to descend to ~20 km above the surface, release a paraglider chute, take the next hour to take a transcect of images across the surface, and then have 1.5 hours on the surface.

The frustration of understanding anything about the geology of the Venera Lander sites is the utter lack of geologic context for the surface panoramas. Three "DIMES" type images, taken at 1, 5 and 20 (for example) kilometers with a 45 degree field of view, from my perspective, is almost mandatory for any understanding of the geologic context of chemical/minerological measurements from a lander.

It's lack -- we've only approximately located the landing sites of Venera 8, 9 and 10, 13 and 14, and Vega 1 and 2 -- in providing real geologic context has led to essential uncertainty on what geology some of those landers are on. Some are just not well located in regions of complex geology, Venera 8 in particular.

Radar data, by it's inherent nature, tells a lot about surface materials physical configuration: relief, roughness, texture, internal scattering, etc, but almost nothing about chemistry. In addition, it's remarkably hard at times to relate to visible geology. Witness the difficulty in relating optical observations of the Huygens landnig site to radar data. Shuttle radar penetrates a meter or so under sand sheets in the Sahara and show geology underneath you can't see standing there or in visible imagery from orbit. On a mission dominated by geochemistry-science, I'd prefer 3 good descent images over spiffy surface panoramas any time, much as I love a good pan!

Why does not do design a good space architecture as the Mars ones with the initial support of MGS and Odyssey as the initial recoconizance support and as relay for the landed probes to Earth?

This architecture should be applied for the next mission to Venus and it would solve the communications problems to landed probes on Venus and also a better understanding of Venus in order to even assure the future missions to Venus. This mission be must taken with a gradual steps, perhaps, an lapse of 10 years.

Why does not do design a good space architecture as the Mars ones with the initial support of MGS and Odyssey as the initial recoconizance support and as relay for the landed probes to Earth?

This architecture should be applied for the next mission to Venus and it would solve the communications problems to landed probes on Venus and also a better understanding of Venus in order to even assure the future missions to Venus. This mission be must taken with a gradual steps, perhaps, an lapse of 10 years.

Rodolfo

An orbiter for COM abilities would not have as much value for a world where landed missions only last two hours. In fact, an orbiter would be almost pointless, because it would only get to fly over the landing site once or twice while the lander was alive! You may as well land the COM package on the lander and send the high-gain telemetry straight to Earth instead of having it spend 90% of the lander's mission out of line of sight with the instruments on the surface.

An orbiter for COM abilities would not have as much value for a world where landed missions only last two hours. In fact, an orbiter would be almost pointless, because it would only get to fly over the landing site once or twice while the lander was alive! You may as well land the COM package on the lander and send the high-gain telemetry straight to Earth instead of having it spend 90% of the lander's mission out of line of sight with the instruments on the surface.

Let me see the architecture space design. As Venus rotates more than one year Earth. So the desired landing site can be programmed with anticipation according to the Earth's departure. So the lander will stay *almost on the same place facing to the Earth* for a long time so its HGA would be useful without much worries about pointing to Earth. So it is reasonably understandable that the COM orbiter is pointless unless a special or restrict conditions such as to land on the Sun's face.

Now, I am not very convinced that with our actual technology can permit to last the instruments less than 2 hours in Venus. It might be due to the economics factors. The cheaper ones will last less time than ones with more robust and expensive equipement incorporated with any kind of thermal refrigeration (LOX, LH, RTG, others).

Up to know, I don't still see a clear objective for the next mission to Venus. Indeed, it is still to early or not. The depending upon to the mission objective, It will be the factor influence for the right space architecture design. One group support for a ballute, others support for a landing of multiple probes. Any of them are useful but they bring the results for different objectives.

I take for granted that the first three or four geological Venus landers will carry cameras. The question is just how many landers will be sent to other parts of the planet afterwards, and how many of them should also carry cameras. And since Venus (let's face it) is not burningly high on America's list of space priorities, it will be a long time before this question even becomes relevant.

The near-term question that IS relevant is whether we should send off a few geological landers right now (a la SAGE), or whether we should wait until we do a little more orbital reconnaissance (with radar and/or near-IR), after Venus Express, to select good landing sites for them. I don't begin to know enough science to judge this question, but I'll be interested in hearing what the VEXAG people say shortly.

A possible Venus exploration gizmo: either an aerobot or a stationary lander that needed a source of artificial light to do spectroscopy despite the incessant IR glow [...]

A bit of terrestrial exploration of Venus: Christophe Pellier's images of Venus's nightside in the 2004 section overexpose the dayside in IR and you can faintly make out the nightside glowing from the surface heat!

There have always been rumors of people seeing an "ashen light", seeing exactly this sort of spectacle, with the eye. Well, 1000 nm is certainly beyond the abilities of human detection, and I'm highly skeptical that anyone could see this with their own rods and cones.

A bit of terrestrial exploration of Venus: Christophe Pellier's images of Venus's nightside in the 2004 section overexpose the dayside in IR and you can faintly make out the nightside glowing from the surface heat!

There have always been rumors of people seeing an "ashen light", seeing exactly this sort of spectacle, with the eye. Well, 1000 nm is certainly beyond the abilities of human detection, and I'm highly skeptical that anyone could see this with their own rods and cones.

I suppose it might be possible - a few people can hear much higher frequencies than the average person. It doesn't seem too far fetched that we'd get the occasional genetic abnormality that would alter a person's visual spectrum slightly. But granted, stretching it all the way to 1000nm may be a bit much.

I suppose it might be possible - a few people can hear much higher frequencies than the average person. It doesn't seem too far fetched that we'd get the occasional genetic abnormality that would alter a person's visual spectrum slightly. But granted, stretching it all the way to 1000nm may be a bit much.

Well, it's not only how far out 1000nm is, but the fact that normal people have a greatly diminished sensitivity even at red. You can see a red laser in a dark room, sure, but a dim red light is much harder to see a dim green light of the same energy. Rods are only slightly sensitive to red light (they have about the same response curve peak as green-sensitive cones)... and when it comes to detecting *dim* red that happens to be right next to dazzling bright white (!) I am *very* skeptical. If the night side of Venus were somehow isolated from that bright crescent, I might believe it. Put another way, someone orbiting over the night side of Venus would have a much better chance of looking down and seeing non-black than someone on Earth looking into the bright crescent and seeing *dim* dark, near IR.

If the light reflected off Venus can cast shadows on Earth, then Earthshine must similarly illuminate the night side of Venus (remember the Clementine Lunar night-side shots, with the Solar corona and various planets in view, and think, if you will, how *dark* the surface really is compared to the white clouds covering Venus). Of course, at closest approach Venus is 100x further away than the Moon, so the effect will always be somewhat less...

If the Ashen Light waxes and wanes with Terrestrial cloud cover, then the case is settled (that phenomenon is visible on the Moon, and has been used to estimate changes in the overall albedo of the Earth).

I wonder whether Venus Express will be able to image the clouds of Venus by Earthshine?

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted.
Do not reproduce without permission. Read
here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the
individual posters and do not necessarily reflect the opinions
of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer
UnmannedSpaceflight.com moderation team is wholly independent
of The Planetary Society. The Planetary Society has no influence
over decisions made by the UnmannedSpaceflight.com moderators.

SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society
and is funded by donations from visitors and members. Help keep
this forum up and running by contributing
here.